Recent questions tagged assembly

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assembly - Removing Spaces from String in MIPS

I am currently trying to write a code that takes in a string and outputs that same string with no spaces. Everything in my code currently works, but ... syscall end: #end program li $v0, 10 syscall #end See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - How is it possible that BITWISE AND operation to take more CPU clocks than ARITHMETIC ADDITION operation in a C program?

I wanted to test if bitwise operations really are faster to execute than arithmetic operation. I thought they were. I wrote a small C program to ... takes longer on average than the arithmetic operator. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - 32-bit extended multiplication via stack

This is the code I have been using to implement extended multiplication of two 32-bit numbers. Is there a way to implement the similar logic by making a ... 1 dec cl jnz checkbit mov ax, 0x4c00 int 0x21 See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - NASM - How do you move an 8-bit register into a full 32-bit register?

I am writing NASM assembly code, and have to do some indexed addressing. I have the index stored in $al, but x86 won't let you use $al as an ... ecx] ; value_at(first_table_addr + char) -> bx pop ecx See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - X86 IDIV sign of remainder depends on sign of dividend for 8/-3 and -8/3?

Can anyone explain for me why the sign of the remainder is different in these cases? Is this an emulator bug or do real CPUs do this, too? 8 / -3 : quotient( ... / 3 : quotient(AL) = -2 remainder(AH) = -2 See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Using 8-bit registers in x86-64 indexed addressing modes

Is it possible to use the 8-bit registers (al, ah, bl, bh, r8b) in indexed addressing modes in x86-64? For example: mov ecx, [rsi + ... pointed towards basically the same answer as above: probably not. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Difference between MOV r/m8,r8 and MOV r8,r/m8

By looking at intel volume of instructions, I found this: 1) 88 /r MOV r/m8,r8 2) 8A /r MOV r8,r/m8 When I write a line like this in NASM, ... option two? if so, on what basis did NASM chosed the first? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Is there any way to write for Intel CPU direct core-to-core communication code?

I want to ping threads to all cores in two CPU socket, and write communications between the threads without write back to DRAM. Write ... forums/intel-moderncode-for-parallel-architectures/topic/700477 See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Compile ASM and C with ASM for debugging

I have two small files that I want to compile in CMake for debugging it with CLion and GDB main.c int my_strlen(char *); int main() { printf("Test: ... in a C project and compile with a CMakeList.txt ? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - RISC-V build 32-bit constants with LUI and ADDI

LUI (load upper immediate) is used to build 32-bit constants and uses the U-type format. LUI places the U-immediate value in the top 20 ... good implementation to move a 32bits immediate to register? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - invalid effective address calculation

Please look at the following program, the error is invalid effective address calculation and i have mentioned that line please tell me why its invalid effective ... jmp loop end: mov ax,0x4c00 int 0x21 See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Why does syscall compile in NASM 32 bit output while popa does not compile in 64 bit?

The Intel manual says that: the syscall instruction is invalid for compatibility mode (32-bit) popa is invalid for 64-bit mode So is there a reason why NASM ... 09 on Ubuntu 14.04 (should be OS agnostic). See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - What does it mean that "registers are preserved across function calls"?

From this question, What registers are preserved through a linux x86-64 function call, it says that the following registers are saved across function calls: ... much in explaining what I may be missing. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Hello world in NASM with LINK.EXE and WinAPI

I'm trying to get a simple Hello world program in NASM to run. I want to print to the console without using C-Libraries, interfacing directly with ... What am I doing wrong? EDIT: Fixed calling convention See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - ARM AArch64 stack management

Is there no ability to have a 64 bit stack for ARMv8? I understand there is no push and pop instructions on AArch64 so is stack management left ... how function calls will work when operating in AArch64. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Print a number in NASM - building an x86 Bootsector

I just started messing around with assembly language and I tried to print the number 9 on console. Here is what I wrote: global _main section .data ... interrupt. So, what interrupt code should I use? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Does x64 support imply BMI1 support?

It it safe to assume that x64 builds can use TZCNT without checking its support through cpu flags? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - use slt to check unsigned integer addition carry flag mips

I'm new to Assembly and I know this is a fair easy question. I supposed to do unsigned integer addition for $a0 and $a2 and store the result in ... this is gonna to work. Any help would be appreciated. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Why does GCC chose dword movl to copy a long shift count to CL?

In the third chapter of Computer System: A Programmer's Prespective, an example program is given when talking about shift operations: long shift_left4_rightn( ... , %ecx" when dealing with long integer. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Multiplying 32 bit two numbers on 8086 microprocessor

I have code example for multiplying two 16 bit numbers on 8086 and trying to update it for two 32 bit numbers multiplying. start: MOV AX,0002h ; ... to use any register arbitrarily? Thanks in advance. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - What is the "relationship" between addi and subi?

I'm supposed to answer this question. After some research it says that add and sub have the same opcode and differ only in the functional field. Is this ... 2009 subi is implemented as addi rB, rA, -IMMED See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - EMU8086 dividing 32 bit number by a 16 bit number gives unexpected 0 remainder

I was trying to divide (Unsigned) 8A32F4D5 by C9A5 using emu8086 tool. I expected the quotient to be AF73H and the remainder be 94B6H. After writing the ... 21H MAIN ENDP END MAIN The output in EMU8086: See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - NASM x86_64 scanf segmentation fault

I am new to nasm and I really want to learn how to store a number with user input. I can't get rid of getting segmentation fault when using ... push number push format call scanf ret Thanks in advance! See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - why cannot define same local label in multiple functions?

Want to define same local label in multiple functions: .text .globl main func: push %rbp mov %rsp, %rbp .a: leave ret main: push %rbp mov %rsp, ... labels in multiple functions. Do you have any clues? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Why any modern x86 masks shift count to the 5 low bits in CL

I'm digging into left and right shift operations in x86 ASM, like shl eax, cl From IA-32 Intel Architecture Software Developer's Manual 3 All IA-32 ... 1 cycle? Any detailed explanation would help a lot! See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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520 views

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assembly - INT 13, 2 hanging on x86 real mode when trying to read sectors from floppy drive

I'm writing a DOS clone for a school project and I'm trying to read some sectors from a floppy drive (mainly the root directory of a FAT12 file system, ... that would be useful that I've not posted here? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - About the memory layout of programs in Linux

I have some questions about the memory layout of a program in Linux. I know from various sources (I'm reading "Programming from the Ground Up") ... why I get the segmentation fault earlier at 0x804a000? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Switch from protected mode to real mode in a DOS EXE program

I learned to switch to protected mode with a simple DOS based bootloader. This loader loads kernel.bin into a buffer and copies the buffer to 100000h (kernel ... ] sti mov ax,4c00h ;Exit process int 21h See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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